The objective of this proposal is to investigate the degree of lymphocyte heterogeneity in normal mice and in mice with immunologic disorders, by using the ability of various strains of bacteria to bind to mouse lymphocyte sub-populations. Lymphocyte-binding mutants of non-pathogenic bacterial strains will be obtained to further investigate lymphocyte heterogeneity. After establishing which bacteria bind to mouse lymphocytes, various combinations of two bacteria will be tested to determine whether they bind to the same subset or to different subsets of lymphocytes. By analyzing the data from the various combinations of bacteria, a "lymphocyte subpopulation map" will be constructed for several lymphoid organs. Preliminary data, based on the pattern of binding of eight bacterial strains, indicates that mouse splenic lymphocytes can be divided into at least 3 B cell and 3 T cell subpopulations. The molecules involved in the interaction between lymphocytes and bacteria will be isolated by standard biochemical techniques. The functions of the lymphocyte subpopulations will be determined by testing the isolated subpopulations in various immunological assays.